Abstract
Floral scent is a key mediator in many plant–pollinator interactions. It is known to vary not only among plant species, but also within species among populations. However, there is a big gap in our knowledge of whether such variability is the result of divergent selective pressures exerted by a variable pollinator climate or alternative scenarios (e.g., genetic drift). Cypripedium calceolus is a Eurasian deceptive lady’s-slipper orchid pollinated by bees. It is found from near sea level to altitudes of 2500 m. We asked whether pollinator climate and floral scents vary in a concerted manner among different altitudes. Floral scents of four populations in the Limestone Alps were collected by dynamic headspace and analyzed by gas chromatography coupled to mass spectrometry (GC/MS). Flower visitors and pollinators (the subset of visitors with pollen loads) were collected and identified. Preliminary coupled gas chromatographic and electroantennographic measurements with floral scents and pollinators revealed biologically active components. More than 70 compounds were detected in the scent samples, mainly aliphatics, terpenoids, and aromatics. Although several compounds were found in all samples, and all samples were dominated by linalool and octyl acetate, scents differed among populations. Similarly, there were strong differences in flower visitor spectra among populations with most abundant flower visitors being bees and syrphid flies at low and high altitudes, respectively. Pollinator climate differed also among populations; however, independent of altitude, most pollinators were bees of Lasioglossum, Andrena, and Nomada. Only few syrphids acted as pollinators and this is the first record of flies as pollinators in C. calceolus. The electrophysiological tests showed that bees and syrphid flies sensed many of the compounds released by the flowers, among them linalool and octyl acetate. Overall, we found that both floral scent and visitor/pollinator climate differ among populations. We discuss whether interpopulation variation in scent is a result of pollinator-mediated selection.
Highlights
Handling editors: Isabel Alves dos Santos and Isabel Machado.Department of Ecology and Evolution, Plant Ecology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, AustriaDepartment of Biological Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo, ItalyCentro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale “Bosco Fontana”, Marmirolo, ItalyThe majority of angiosperms is pollinated by animals, mostly insects (Ollerton et al 2011)
The pollinator climate of a plant species often varies among populations and potentially contributes to the evolution of pollination ecotypes, i.e., forms adapted to the local pollinator fauna, especially if differences in the pollinator climate among populations are temporally and spatially stable in an evolutionary timescale (Johnson 2006)
A SIMPER analysis was used to determine the compounds most responsible for variation in scent among populations, and PERMDISP was used to test for differences in dispersion of semi-quantitative floral scent data among populations (10,000 permutations), both using Primer 6.1.16
Summary
Handling editors: Isabel Alves dos Santos and Isabel Machado.Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale “Bosco Fontana”, Marmirolo, ItalyThe majority of angiosperms is pollinated by animals, mostly insects (Ollerton et al 2011). The pollinator climate (composition, abundance, and efficiency of pollinators; Grant and Grant 1965) of a plant species often varies among populations and potentially contributes to the evolution of pollination ecotypes, i.e., forms adapted to the local pollinator fauna, especially if differences in the pollinator climate among populations are temporally and spatially stable in an evolutionary timescale (Johnson 2006). Such ecotypes often differ in floral characteristics which allow recognizing subspecies or other intra-specific taxa (e.g., Johnson 1997). Olfactory cues are most important for plants pollinated at night (Cordeiro et al 2017; Dobson 2006; Dötterl et al 2012), and for highly specialized pollination systems (Heiduk et al 2016; Milet-Pinheiro et al 2013; Schäffler et al 2015; Schiestl et al 1999)
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